Presently available boats are frequently equipped with relatively sophisticated electronic equipment including video depth sounders, radars, automatic pilots, loran-c receivers and the like which basically are constructed to operate with a voltage supply between 11 and 14 volts DC. It is also well known that when the engine of a boat is started by using the electric starting motor, a voltage drop occurs inasmuch as the electric starting motor consumes a large portion of the electrical energy available from the storage batteries which is usually a 12 volt battery providing electrical energy to a conventional 12 volt DC electrical system found on most present day boats, with the electronic equipment operating between 11 and 14 volts DC. While the voltage supply between 11 and 14 volts is adequate to maintain the electronics operational, when a boat's engine is being started, the voltage drop to 9 volts or less which can cause many marine electronic components to shutdown or freeze operation especially the components found on present day boats. When this occurs, some of the electronic equipment requires several minutes to warm up and commence proper operation thereby causing the operator significant inconvenience. For example, many video depth sounders need to be set to the proper mode and depth scale each time they are powered up and some autopilots may freeze operation if a voltage drop occurs when in operation thus requiring the equipment to be shut off and switched back on again before normal operation can resume. It is also well known that frequently the boat's engines need to be re-started after the electronic equipment has been previously powered up such as when stopping for fuel or fishing at several different locations on a single outing. The Coast Guard and other law enforcement agencies rely heavily upon radar. This instrument is likewise liable to be lost temporarily after the vessel has stopped for boarding otherwise and when the engines are restarted. Presently, a system is required that will maintain adequate voltage to the electronic components of a boat or other vehicle in order to provide continuous operation during repeated starts.
Efforts have been made to provide auxiliary or alternative power sources to supply electrical energy to a load in response to various load conditions. However, although conventional techniques use alternative power sources and devices are provided for maintaining a predetermined voltage supply, such techniques do not disclose the specific circuit arrangement for automatically switching a load from one power source to another and isolating the loads and power sources including the specific relationship of the primary and secondary batteries and electronic components incorporated into this invention. None of the known devices allow the electronic accessories of a boat or other vehicle to remain fully charged during momentary operation of the engine starter.